Researchers have developed a miniature superconducting thermometer that measures temperatures below 1 kelvin (-272.15 °C or -457.87 °F), down to 50 millikelvin (mK) and potentially 5 mK. It is smaller, faster, and more convenient than conventional cryogenic thermometers for chip-scale devices and could be mass-produced.
Measuring 2.5 × 1.15 millimeters in size, the thermometer can be embedded in or stuck to another cryogenic microwave device to measure its temperature when mounted on a chip. The thermometer was used to demonstrate fast, accurate measurements of the heating of a superconducting microwave amplifier.
The thermometer allows researchers to measure the temperature of a wide range of components in test packages at very little cost and without introducing a large number of additional electrical connections. This has the potential to benefit researchers working in quantum computing or using low-temperature sensors in a wide range of fields.
The thermometer consists of a superconducting niobium resonator coated with silicon dioxide. The coating interacts with the resonator to shift the frequency at which it naturally vibrates. Scientists suspect this is due to atoms “tunneling” between two sites, a quantum-mechanical effect.
The thermometer is based on a new application of the principle that the natural frequency of the resonator depends on the temperature. The thermometer maps changes in frequency, as measured by electronics, to a temperature. By contrast, conventional thermometers for sub-Kelvin temperatures are based on electrical resistance. They require wiring routed to room-temperature electronics, adding complexity and potentially causing heating and interference.
The new thermometer measures temperature in about 5 milliseconds — much faster than most conventional resistive thermometers at about one-tenth of a second. The thermometers are also easy to fabricate in only a single process step. They can be mass-produced, with more than 1,200 fitting on a 3" (approximately 75-millimeter) silicon wafer.